Gas distributing arrangement for fluidized solids vessels



Max-c113, 1959 F, u c u c ETAL 2,876,079

GAS DISTRIBUTING ARRANGEMENT FOR FLUIDIZED SOLIDS VESSELS Filed March 7, 1956 2 Sheets-Sheet 1 AIR FIG I Edward F.. Upchurch Edward C. Luckenbach Bv (i. 6L. M Attorney Inventors March 1959 E. F. UPCHURCH ETYAL 2,876,079

GAS DISTRIBUTING ARRANGEMENT FOR FLUIDIZED SOLIDS VESSELS Filed March '7, 1956 2 Shee ts-Sh'eet 2 GRID a B0 GRID A FIG-2 -s BYPASSED Edward F. Uphufch Edward C. Luckenbach By 1. M Attorney United States Patent GAS'DISTRIBUTING ARRANGEMENT FOR FLUIDIZED SOLIDS VESSELS Edward F. Upchurch, Fanwood, and Edward C. Luckenbacll, Roselle Park, N. J., assignors to Esso Research and Enginering Company, a corporation of Delaware Application March 7, 1956, Serial No. 570,156

5 Claims. (Cl. 23-284) This invention relates to improved apparatus and process associated therewith for contacting fluidized solids with gasiform fluids. The invention pertains more particularly to a vessel wherein finely divided solids, either catalytic or, non-catalytic, are fluidized and treated or reacted with liquid "or gaseous fluids. .This invention proposes an improved gas distributing arrangement or grid design for supporting, and for uniformly distributing a gasiform fluidizing agent and/ or reactant throughout, a fluidized solids bed within a reaction vessel. It has particular applicability to high temperature fluidized solids processes. I

In brief compass, this invention proposes to place in a fluidized solids vessel, a plurality of substantially hori' zontal, vertically spaced, perforated, fixed gas distributing members adapted to support a bed of fluidized solids. These gas distributing members ofier upwardly decreasing graduated resistance to the. flow of fluidizing gas there.- through. Associated with the plurality of perforated members or grids-are conduits for admitting controlled amounts of a fluidizing and/ or reactant gas between each of the grids and beneath the lowest grid.

This invention will find use in various fluidized solids processes such as ore roasting, drying of wet solids, coal carbonization or burning for power generation. shale retorting, catalytic cracking of gas oils, reforming of heavy naphthas, and coking of heavy oils. it has particular utility in the burning of carbon-containing solids wherein relatively high temperatures are encountered, such as in the regeneration of spent cracking or hydroforming catalyst. It is especially adapted to the partial burning of particulate fluid coke used as a heat carrier in a hydrocarbon oil fluid coking process for sup plying heated solids to the reaction zone, and will be described in relation to this fluid coking process.

In the fluid coking process, as used in the petroleum industry, a heavy oil-usually a low value residual oil, shale oil, asphalt, etc.--is converted by pyrolysis to relatively lighter hydrocarbons and coke by contact with fluidized finely divided heat carrying solids maintained at a coking temperature in the range of 850 to l600 R, or above. The coke produced by the pyrolysis deposits on the fluidized solids, layer by layer, and becomes a part thereof. The heat carrying solids normally used are coke particles produced by the process, but other types of solids can be used such as sand, spent catalyst, and metal particles.

Heat is supplied to the coking zone by withdrawing carbon containing solids from the coking zone and partially burning them as a fluidized bed in a burning zone, whereby their temperature is raised 100 to 400 F. above the coking temperature. The solids so heated are then returned to the coking zone.

This invention is concerned with an improved grid design for supporting the fluid bed within the burning zone, and for uniformly distributing the combustion air throughout the bed.

ice

ln fluidized solids operations it is usually essential that the fluidizing gas, which may also be a reactant, be properly distributed as it enters the fluid bed. Also, it is important that the finely divided solids of the bed do not fall below the grid because this may establish recirculation of the solids through the grid and severely erode it. besides causing a decrease in the efliciency of contacting by permitting solids to settle out below the grid. When high carbon-containing solids are being burned, such as fluid coke particles, the problem of solids falling below the grid is even more severe because the carbon-containing solids may burn in a non-fluidized state beneath the grid and cause local hot spots which result in metal oxidation and distortion. Also, if the gas distributing grid is not properly designed, part of the grid may become plugged by the fluidized particles, resulting in maldistribution of the fluidizing gas.

The gas distributing grids previously used have been designed such that the perforations or openings in the grid, i. e., the free area of the grid, were sufficient to maintain a high pressure drop (gas velocity over the grid to prevent any significant amount of the solids from passing down through the grid. It has been-found that this design is relatively inflexible because it does not readily permit'ariy substantial variation in the rate of flow of the fluidizing gas, i. e., fluidizing gas rate turndown.

It has been found, for example, in hydrocarbon fluid coking operations, that there may be wide seasonal variations in the supply of feed stock to the coking vessel. For example, a coker designed to convert a maximum of 10,000 barrels per day of residual oil, may be called upon during the. winter. months to convert only 4,000 barrels per day. This means that the burner vessel associated with the coking vessel 'for heating the solids must operate during the winter months at a capacity far below design, 1'. e., at very low air rates. At these low air rates, the pressure drop over the air distributing grid is insuflicient to prevent backflow of the coke particles undergoing burning, and this may result in damage to the vessel. 7

One way of maintaining a high pressure drop over the gas distributing grid is to make the openings or free area of the grid variable. This may be done by using a single grid with a perforated rotatable section mounted above or below it, and asclose to it as mechanical limitations will permit. This rotating section may encompass all or part of the fixed grid. Rotating this section will change the alignment of the holes between the plates such that the pressure drop can be varied. However, because of the air distribution problem and mechanical problems, e. g. binding because of the close vertically spaced arrangement, associated with this rotating section, it is not an attractive arrangement.

The present invention-proposes an improved gas distributing arrangement using-two or more fixed grids or foraminous plates, which overcomes these and other difficulties. This novel gas distributing arrangement adequately allows for variations in the fluidizing gas rate. while maintaining a pressure drop suflicient to prevent solids falling down through the distributing means.

In the drawings, Figure 1 illustrates a fluidized solids vessel, e. g., a fluid coke burning vessel, containing the gas distributing means proposed by this invention. Figures 2 and 3 illustrate alternative embodiments of this invention, differing from Figure l primarily in the method by which the fluidizing gas is admitted to the vessel.

In all designs, a double grid arrangement is shown but it will be apparent to those skilled in the art that three or more grids of graduated resistance to the flow of gases may be used. As illustrated in the drawings, the upper grid has a greater number and/or size of holes such that it has the greatest free area, and thus the least resistance to the flow of gases. During normal or high capacity operation, a portion of the fluidizing gas supplied to the vessel is admitted between the grids, and a portion of the fluidizing gas passes through the lower grid. In this manner the total pressure drop over the gas distributing arrangement of this invention is effectively and readily controlled. At maximum fluidizing gas flow rate, the fluidized bed rests upon the upper grid and at minimum rates, it rests upon the lower grid.

Referring now to Figure 1, vessel 1 contains a fluidized bed 2 of particulate fluid coke particles having an upper level 3. Coke from the coking process is admitted to bed 2 by line 19 and heated coke is withdrawn and circulated to the process by line 20. The combustion gases emerge from the bed and are removed overhead via line 4 after having entrained solids removed in cyclone system 5. Air to support burning of the fluid coke particles is supplied to the lower part of evssel 1 by line 6. In this particular arrangement, line 6 comprises an upwardly open ing gas inlet conduit that terminates beneath the grid arrangement. A downwardly turned gas distributing cap 7 is vertically spaced from the end of conduit 6 and encompasses it as shown. This distributing cap serves to distribute the air, and acts as a seal to prevent coke particles from flowing down into conduit 6 when air is not flowing. The air admitted by line 6 to the vessel initially is distributed by lower grid 8 which has the lesser free area, and then passes through upper grid 9. Control means are provided for bypassing some of this air through lower'grid 8 to space between grids 8 and 9. This by pass arrangement comprises one or more conduits 10 having-associated therewith flow control means or valves 11 which can be operated externally of vessel 1.

During low capacity operation, conduits 10 are closed and all the air passes up through grid 8 and then through grid 9. During high capacity operation, conduits 10 are partly or wholly opened so that a substantial proportion of the air bypasses the lower grid 8 whereby the total pressure drop over the grids can be maintained substan tially constant.

' If desired for mechanical reasons, the two grids may be cast as one piece with suitable spacers and supports in between the grids to arrive at a rigid structure. Other means, of course, may be used to support the two grids.

Figure 2 illustrates another means of admitting the bypass air between the grids. Like parts in the drawing have the same number as in Figure 1. This design'uses a double grid but has. the advantage of not needing movable parts inside the vessel. At the higher air rates, the bypass fluidizing gas is admitted between grids 8 and 9 by conduit system 12 which may comprise, for example, a manifold system terminating in a multiplicity of small uniformly spaced outlet conduits 13. The amount of gas supplied byline 12 is, of course, controlled externally of the vessel by means not shown.

It will be apparent to those skilled in the art that the design of Figure 2, and that of Figure 3, will permit the admission of different types of gases to the fluidizing vessel. For example, when this invention is applied to the fluid hydroforming process, certain significant ad vantages other than those described can be realized. As known in the art, the fluid hydroforming process comprises the contacting of a vaporized naphtha feed with a conversion catalyst (e. g., one containing platinum or molybdenum, etc. on suitable support) in the presence of a hydrogen which is usually a recycled hydrogencontaining gas. This recycled hydrogen is highly superheated to supply a part of the necessary heat for the reaction. It is desirable to avoid mixing this heated recycled hydrogen with the vaporized naphtha feed until they are introduced into the fluidized catalyst bed. According to this invention, the heated recycled gas can be admitted to the reaction vessel by line 6, and all or part 4 of the vaporized naphtha feed can be admitted by line 12 in between the two grids. Uniform distribution and mixing is assured, and the mixing does not occur until just before the reactants enter the fluid bed, whereby unnecessary detrimental thermal cracking of the vaporized naphtha is avoided.

Referring to'Figure 3, another arrangement for admitting the fluidizing gas is shown, similar to that of Figure 2. This design has the advantage of simpler construction and symmetrical air distribution beneath the upper grid. As shown, the bypassed fluidizing gas is ad mitted by a conduit 13 that extends from within conduit 6 through distributing cap 7 and grid 8, and terminates beneath the upper grid 9. As with conduit 6, a gas dis tributing cap 14 is associated with conduit 13. At high capacity operation, a portion of fluidizing gas is admitted between the grids by line 13.

Also shown in Figure 3 are alternative means of supporting the grids. Instead of supporting the grids directly from the vessel walls as by lugs or clips, a skirt arrangement may be used to permit thermal expansion and contraction, and to provide a positive seal against gases bypassing the grids. This skirt arrangement may comprise, for example, a circular member 15 that encompasses the grids and initiates from the vessel walls above the grids such that the grids are dependent thereon, or may comprise a similar vertical skirt 16 that initiates from the vessel walls beneath the grid such that the grids are supported thereby, as illustrated by the sectional'views shown in Figure 3..

Example The following specific example describing a commercial sized fluid coke burning unit, used to supply heated coke particles to a hydrocarbon oil fluid coking vessel, will serve to make this invention clear. The example refers specifically to Figure 3.

internal vessel diameter- 21 feet. Number of gas distributing grids 2 1 inches. 3 feet 6 inches.

Grid thickness Grid spacing Free area, upper grid 1" dia. holes) 1 67.4%. Free area, lower grid (120 dia. holes) I 32.6%.

70 to 750 microns. 11.7 tons/min. 45 lbs./cu. ft.

Coke size range Coke circulation rate Fluid bed density Total coke holdup 60 tons. Bed temperature 1125 F. Pressure cyclone inlet--- 6 p. s. i. g. Air inlet temperature 250 F.

Min. air rate (bed supported on lower grid) Max. air rate (bed supported on upper grid) Air flow for 50% max. air

rate:

9,500 S. C. F. M.

21.600 S. C. F. M.

Admitted below grids- 85%. Admitted between grids 15%. AP over low grid 1.48 p. s. i. .\P over upper glid 0.52 p. s. i.

What is'claimecl is:

1. Apparatus for contacting tluidizable solids and gases which comprises a vertically disposed vessel, outlet means in the upper portion for removing gases, gas distributing means in said vessel adapted to support a fluidized bed of solids, said gas distributing means comprising a plurality of vertical spaced foraminous plates, each plate having a multiplicity of relatively uniformly spaced openings across its bed supporting cross section, and said plates having graduated free areas to the passage of gases, the upper of said plates having the greatest free cross-sectional area such that pressure drop due to the flow of gases therethrough is the lowest, and distinct gas inlet means other than said foraminous plates adapted to admit gases beneath and between said plates.

2. In a fluidized solids vessel, a plurality of substantially horizontal, vertically spaced, perforated, fixed gas distributing members adapted to support a bed of fluidized solids therein, each of said members being perforated in a substantially uniform manner across its bed supporting cross section, said plurality of distributing members being constructed so that the perforations of the upper distributing member define a greater free cross-sectional area than that defined by the perforations of the lower distributing member, the members thus offering upwardly decreasing graduated resistances to the flow of gas therethrough, in combination with distinct inlet means other than said gas distributing members for admitting gas between each of said members and beneath the lowest.

3. Apparatus of claim 2 wherein said means for admitting gas between each of said members comprises a conduit and variable gas flow restriction associated therewith communicating with the space in said vessel below the lowest of said members and the space between said members.

4. Apparatus of claim 2 wherein said means for admitting gas between each of said members comprises a gas manifold communicating through the side of said vessel with a controlled source of gas supply.

5. The apparatus of claim 2 wherein said means for admitting gas between said members and beneath the lowest, comprises an upwardly opening vertical gas inlet conduit entering the bottom of said vessel and terminating beneath the lowest of said members, a downwardly turned gas distributing cap in vertical spaced relation to and encompassing the upper end of said gas inlet conduit, a second upwardly opening vertical gas inlet conduit extending from within said first named conduit, through said gas distributing cap and the lowest of said members, and terminating beneath the member next above the lowest of said members, and a second downwardly turned gas distributing cap in vertical spaced relation and encompassing the upper end of said second gas inlet conduit.

References Cited in the file of this patent UNITED STATES PATENTS 

1. APPARATUS FOR CONTACTING FLUIDIZABLE SOLIDS AND GASES WHICH COMPRISES A VERTICALLY DISPOSED VESSEL, OUTLET MEANS IN THE UPPER PORTION FOR REMOVING GASES, GAS DISTRIBUTING MEANS IN SAID VESSEL ADAPTED TO SUPPORT A FLUIDIZED BED OF SOLIDS, SAID GAS DISTRIBUTING MEANS COMPRISING A PLURALITY OF VERTICAL SPACED FORAMINOUS PLATES, EACH PLATE HAVING A MULTIPLICITY OF RELATIVELY UNIFORMLY SPACED OPENINGS ACROSS ITS BED SUPPORTING CROSS SECTION, AND SAID PLATES HAVING GRADUATED FREE AREAS TO THE PASSAGE OF GASES, THE UPPER OF SAID PLATES HAVING THE GREATEST FREE CROSS-SECTIONAL AREA SUCH THAT PRESSURE DROP DUE TO THE FLOW OF GASES THERETHROUGH IS THE LOWEST, AND DISTINCT GAS INLET MEANS OTHER THAN SAID FORAMINOUS PLATES ADAPTED TO ADMIT GASES BENEATH AND BETWEEN SAID PLATES. 